JHuck

Hello, this is my first post on OSO. After reading through a number of other posts, I feel confident you guys and gals can help me zero in on an appropriate prop for my set up.

I have a 1995 21' Baja Islander. It is an open bow boat that weighs in around 3,200 lbs (I think). It has an Alpha gen II. It came with a carbed 350 Mag but I recently upgraded to a 383. Dyno figures are 433 hp at 5,500 rpm and 466 ft/lbs at 4,600 rpms. Cam is a mild marine grind 214/218 and I am running GLM manifolds with thru hull exhaust.


I currently spin the prop that was on the boat when I bought it last year, a 14.25 X 21 Turbo 3 blade. With the family, toys and full tank it will run 64 on GPS at 5,600. The boat rides great with my Smart tabs on the lightest setting. The hole shot is strong enough to pop me up on slalom at 3/4 throttle.

Now that it's dialed in, I would really like to hit 70 mph (realizing I will give up some bottom end). I've communicated with Julie regarding using the Laser II line. She seems to think this would be a decent choice for my boat. Now the big question... a 23 or 25P for my set up?

Your thoughts?

Plum_Crazy

I had a similiar hull in a 1988 Baja Sunsport 196. I ran three different levels of power in it, from 280HP all the way to 500HP. I experimented with many different props, including the Laser II, and always ended up with either the standard Mercury Mirage or the Mirage Plus.

The first thing to figure out is where you should run your engine at WOT. Usually, it's closer to the peak torque number. I'd consult with Brett at Bblades. He is very knowledgeable. He also has a program that allows you to try out props.

JHuck

Thanks Plum. I figured things might work out if I put it closer to my peak tq but I've had some tell me this could really put a strain on things, especially the Alpha. Since peak tq occurs at 4600, I wonder if I'd be safe around 5K-5100 rpm. Whichever prop I choose, it won't be for towing but more for running faster/farther on big lakes like Cumberland and Dale Hollow.

bbladesprops

The Laser 2 is a great prop out of the box for speed for the smaller Baja's.

However, this application is different due to the power. In order to harness this, go to the blade area of the Mirage Plus. Let's test a stock propeller and use that base line information to exactly dial in the recipe for your Lab job.

This can only be done by hand...................

Brett

JHuck

Thanks for the input Brett.

Well, a deal came along that I couldn't pass up. I got a new 25 Laser II for $160. I am going to try it as soon as it comes in. If it doesn't give me what I looking for, we'll go to plan B.

onesickpantera

iTrader: (1)

I bet a 23 Mirage Plus will work well. Should drop your rpms down a down a couple hundred and hopefully pick up a couple mph.

Holeinthewater

If you want absolute top end speed run a Mercury "big ear" chopper. Start with a 24 pitch. Since you are running thru-hull exhaust you can run one of these. I have a similar boat and I'm running one on mine. I've tried everything else, nothing comes close to a chopper. Checkout this link, it will explain choppers.

http://69.24.70.63/adamsdock/chopper.html

JHuck

In all my research in the last couple of months, I haven't come across chopper props. What are the design advantages and disadvantages? Are they used mainly for racing? What kind of mph increase did you see compared to a standard prop of the correct pitch and size for your application?

Holeinthewater

Choppers are "over the hub" exhaust props mainly used on outboards in performance applications. They have a small hub which allows for a larger blade area within a given diameter which increases performance. They are designed to be run near the surface, but perform just as well when submerged, such as on an I/O. They have a lot of bow lift and actually the blade shape is very similar to a blade on a LaserII or Mirage. They tend to cavitate a lot on startup (which makes them impractical for most heavy boats), but once on plane you'll notice an increase in handling and speed. In my boat which is a 93 Baja204(predecessor to the 20 Outlaw) 2400lbs with the 4.3L V6, Alpha One genII I went from 46mph (GPS) with a 23p Mirage to 52mph with the 24p Chopper. I also tried a 25p LaserII and it ran 49mph. I'm currently building a 355 roller small block with aluminum heads and manifolds which should bring me to where you are now in terms of HP. I'll be running the same prop with 1.5:1 gearing and am hoping to run in the low 70's. I noticed the website for that link I gave you is missing the photos. You can go to Mercury's website and see what a Chopper looks like in the racing propeller section.

Marco

fastscarab22

iTrader: (1)

There is guy who has 5 blade solas blade for sale witch is 14 inch instead 14.5 and the 5 blade would make you plane at lower speed and give a little more top end, soceans i think is is name try it